This route is sometimes known as the Sawtooth Ridge Epic.
This ride has it all: old growth forest, pristine lakes, great views, very narrow trail, some climbing challenge, a stretch of flowy downhill and to finish a section of steeper downhill with many switchbacks. Perhaps the one thing missing is an actual peak--despite the name, the route does not go to the top of Osborne Mountain. If you want panoramic views, do the three mile side hike up High Rock that's described below. This is a great ride, more people should check it out.
There are some tough climbs, and there are long, long stretches of very narrow trail with side slope exposure.
The adventure consists of a 11 mile approach on forest roads, and a 12 mile return that's mostly singletrack with a short road climb in the middle. The ride can also be done as a point-to-point shuttle. The shuttle makes it a 12 mile ride that still has 2500 feet of climbing.